sqlite/README.md

SQLite Source Repository

This repository contains the complete source code for the SQLite database engine, including many test scripts. However, other test scripts and most of the documentation are managed separately.

See the on-line documentation for more information about what SQLite is and how it works from a user's perspective. This README file is about the source code that goes into building SQLite, not about how SQLite is used.

Version Control

SQLite sources are managed using Fossil, a distributed version control system that was specifically designed and written to support SQLite development. The Fossil repository contains the urtext.

If you are reading this on GitHub or some other Git repository or service, then you are looking at a mirror. The names of check-ins and other artifacts in a Git mirror are different from the official names for those objects. The official names for check-ins are found in a footer on the check-in comment for authorized mirrors. The official check-in name can also be seen in the manifest.uuid file in the root of the tree. Always use the official name, not the Git-name, when communicating about an SQLite check-in.

If you pulled your SQLite source code from a secondary source and want to verify its integrity, there are hints on how to do that in the Verifying Code Authenticity section below.

Contacting The SQLite Developers

The preferred way to ask questions or make comments about SQLite or to report bugs against SQLite is to visit the SQLite Forum at https://sqlite.org/forum/. Anonymous postings are permitted.

If you think you have found a bug that has security implications and you do not want to report it on the public forum, you can send a private email to drh at sqlite dot org.

Public Domain

The SQLite source code is in the public domain. See https://sqlite.org/copyright.html for details.

Because SQLite is in the public domain, we do not normally accept pull requests, because if we did take a pull request, the changes in that pull request might carry a copyright and the SQLite source code would then no longer be fully in the public domain.

Obtaining The SQLite Source Code

If you do not want to use Fossil, you can download tarballs or ZIP archives or SQLite archives as follows:

• Latest trunk check-in as Tarball, ZIP-archive, or SQLite-archive.

• Latest release as Tarball, ZIP-archive, or SQLite-archive.

• For other check-ins, substitute an appropriate branch name or tag or hash prefix in place of "release" in the URLs of the previous bullet. Or browse the timeline to locate the check-in desired, click on its information page link, then click on the "Tarball" or "ZIP Archive" links on the information page.

To access sources directly using Fossil, first install Fossil version 2.0 or later. Source tarballs and precompiled binaries available at https://fossil-scm.org/home/uv/download.html. Fossil is a stand-alone program. To install, simply download or build the single executable file and put that file someplace on your $PATH. Then run commands like this:

    mkdir -p ~/sqlite
    cd ~/sqlite
    fossil open https://sqlite.org/src

The "fossil open" command will take two or three minutes. Afterwards, you can do fast, bandwidth-efficient updates to the whatever versions of SQLite you like. Some examples:

    fossil update trunk             ;# latest trunk check-in
    fossil update release           ;# latest official release
    fossil update trunk:2024-01-01  ;# First trunk check-in after 2024-01-01
    fossil update version-3.39.0    ;# Version 3.39.0

Or type "fossil ui" to get a web-based user interface.

Compiling for Unix-like systems

First create a directory in which to place the build products. It is recommended, but not required, that the build directory be separate from the source directory. Cd into the build directory and then from the build directory run the configure script found at the root of the source tree. Then run "make".

For example:

    apt install gcc make tcl-dev  ;#  Make sure you have all the necessary build tools
    tar xzf sqlite.tar.gz         ;#  Unpack the source tree into "sqlite"
    mkdir bld                     ;#  Build will occur in a sibling directory
    cd bld                        ;#  Change to the build directory
    ../sqlite/configure           ;#  Run the configure script
    make sqlite3                  ;#  Builds the "sqlite3" command-line tool
    make sqlite3.c                ;#  Build the "amalgamation" source file
    make sqldiff                  ;#  Builds the "sqldiff" command-line tool
    # Makefile targets below this point require tcl-dev
    make tclextension-install     ;#  Build and install the SQLite TCL extension
    make devtest                  ;#  Run development tests
    make releasetest              ;#  Run full release tests
    make sqlite3_analyzer         ;#  Builds the "sqlite3_analyzer" tool

See the makefile for additional targets. For debugging builds, the core developers typically run "configure" with options like this:

    ../sqlite/configure --enable-all --enable-debug CFLAGS='-O0 -g'

For release builds, the core developers usually do:

    ../sqlite/configure --enable-all

Almost all makefile targets require a "tclsh" TCL interpreter version 8.6 or later. The "tclextension-install" target and the test targets that follow all require TCL development libraries too. ("apt install tcl-dev"). It is helpful, but is not required, to install the SQLite TCL extension (the "tclextension-install" target) prior to running tests. The "releasetest" target has additional requiremenst, such as "valgrind".

On "make" command-lines, one can add "OPTIONS=..." to specify additional compile-time options over and above those set by ./configure. For example, to compile with the SQLITE_OMIT_DEPRECATED compile-time option, one could say:

    ./configure --enable-all
    make OPTIONS=-DSQLITE_OMIT_DEPRECATED sqlite3

The configure script uses autoconf 2.61 and libtool. If the configure script does not work out for you, there is a generic makefile named "Makefile.linux-gcc" in the top directory of the source tree that you can copy and edit to suit your needs. Comments on the generic makefile show what changes are needed.

Compiling for Windows Using MSVC

On Windows, everything can be compiled with MSVC. You will also need a working installation of TCL. See the compile-for-windows.md document for additional information about how to install MSVC and TCL and configure your build environment.

If you want to run tests, you need to let SQLite know the location of your TCL library, using a command like this:

    set TCLDIR=c:\Tcl

SQLite uses "tclsh.exe" as part of the build process, and so that program will need to be somewhere on your %PATH%. SQLite itself does not contain any TCL code, but it does use TCL to help with the build process and to run tests. You may need to install TCL development libraries in order to successfully complete some makefile targets. It is helpful, but is not required, to install the SQLite TCL extension (the "tclextension-install" target) prior to running tests.

Build using Makefile.msc. Example:

    nmake /f Makefile.msc sqlite3.exe
    nmake /f Makefile.msc sqlite3.c
    nmake /f Makefile.msc sqldiff.exe
    # Makefile targets below this point require TCL development libraries
    nmake /f Makefile.msc tclextension-install
    nmake /f Makefile.msc devtest
    nmake /f Makefile.msc releasetest
    nmake /f Makefile.msc sqlite3_analyzer.exe

There are many other makefile targets. See comments in Makefile.msc for details.

As with the unix Makefile, the OPTIONS=... argument can be passed on the nmake command-line to enable new compile-time options. For example:

    nmake /f Makefile.msc OPTIONS=-DSQLITE_OMIT_DEPRECATED sqlite3.exe

Source Tree Map

• src/ - This directory contains the primary source code for the SQLite core. For historical reasons, C-code used for testing is also found here. Source files intended for testing begin with "test". The tclsqlite3.c and tclsqlite3.h files are the TCL interface for SQLite and are also not part of the core.

• test/ - This directory and its subdirectories contains code used for testing. Files that end in ".test" are TCL scripts that run tests using an augmented TCL interpreter named "testfixture". Use a command like "make testfixture" (unix) or "nmake /f Makefile.msc testfixture.exe" (windows) to build that augmented TCL interpreter, then run individual tests using commands like "testfixture test/main.test". This test/ subdirectory also contains additional C code modules and scripts for other kinds of testing.

• tool/ - This directory contains programs and scripts used to build some of the machine-generated code that goes into the SQLite core, as well as to build and run tests and perform diagnostics. The source code to the Lemon parser generator is found here. There are also TCL scripts used to build and/or transform source code files. For example, the tool/mksqlite3h.tcl script reads the src/sqlite.h.in file and uses it as a template to construct the deliverable "sqlite3.h" file that defines the SQLite interface.

• ext/ - Various extensions to SQLite are found under this directory. For example, the FTS5 subsystem is in "ext/fts5/". Some of these extensions (ex: FTS3/4, FTS5, RTREE) might get built into the SQLite amalgamation, but not all of them. The "ext/misc/" subdirectory contains an assortment of one-file extensions, many of which are omitted from the SQLite core, but which are included in the SQLite CLI.

• doc/ - Some documentation files about SQLite internals are found here. Note, however, that the primary documentation designed for application developers and users of SQLite is in a completely separate repository. Note also that the primary API documentation is derived from specially constructed comments in the src/sqlite.h.in file.

Generated Source Code Files

Several of the C-language source files used by SQLite are generated from other sources rather than being typed in manually by a programmer. This section will summarize those automatically-generated files. To create all of the automatically-generated files, simply run "make target_source". The "target_source" make target will create a subdirectory "tsrc/" and fill it with all the source files needed to build SQLite, both manually-edited files and automatically-generated files.

The SQLite interface is defined by the sqlite3.h header file, which is generated from src/sqlite.h.in, ./manifest.uuid, and ./VERSION. The Tcl script at tool/mksqlite3h.tcl does the conversion. The manifest.uuid file contains the SHA3 hash of the particular check-in and is used to generate the SQLITE_SOURCE_ID macro. The VERSION file contains the current SQLite version number. The sqlite3.h header is really just a copy of src/sqlite.h.in with the source-id and version number inserted at just the right spots. Note that comment text in the sqlite3.h file is used to generate much of the SQLite API documentation. The Tcl scripts used to generate that documentation are in a separate source repository.

The SQL language parser is parse.c which is generated from a grammar in the src/parse.y file. The conversion of "parse.y" into "parse.c" is done by the lemon LALR(1) parser generator. The source code for lemon is at tool/lemon.c. Lemon uses the tool/lempar.c file as a template for generating its parser. Lemon also generates the parse.h header file, at the same time it generates parse.c.

The opcodes.h header file contains macros that define the numbers corresponding to opcodes in the "VDBE" virtual machine. The opcodes.h file is generated by scanning the src/vdbe.c source file. The Tcl script at ./mkopcodeh.tcl does this scan and generates opcodes.h. A second Tcl script, ./mkopcodec.tcl, then scans opcodes.h to generate the opcodes.c source file, which contains a reverse mapping from opcode-number to opcode-name that is used for EXPLAIN output.

The keywordhash.h header file contains the definition of a hash table that maps SQL language keywords (ex: "CREATE", "SELECT", "INDEX", etc.) into the numeric codes used by the parse.c parser. The keywordhash.h file is generated by a C-language program at tool mkkeywordhash.c.

The pragma.h header file contains various definitions used to parse and implement the PRAGMA statements. The header is generated by a script tool/mkpragmatab.tcl. If you want to add a new PRAGMA, edit the tool/mkpragmatab.tcl file to insert the information needed by the parser for your new PRAGMA, then run the script to regenerate the pragma.h header file.

The Amalgamation

All of the individual C source code and header files (both manually-edited and automatically-generated) can be combined into a single big source file sqlite3.c called "the amalgamation". The amalgamation is the recommended way of using SQLite in a larger application. Combining all individual source code files into a single big source code file allows the C compiler to perform more cross-procedure analysis and generate better code. SQLite runs about 5% faster when compiled from the amalgamation versus when compiled from individual source files.

The amalgamation is generated from the tool/mksqlite3c.tcl Tcl script. First, all of the individual source files must be gathered into the tsrc/ subdirectory (using the equivalent of "make target_source") then the tool/mksqlite3c.tcl script is run to copy them all together in just the right order while resolving internal "#include" references.

The amalgamation source file is more than 200K lines long. Some symbolic debuggers (most notably MSVC) are unable to deal with files longer than 64K lines. To work around this, a separate Tcl script, tool/split-sqlite3c.tcl, can be run on the amalgamation to break it up into a single small C file called sqlite3-all.c that does #include on about seven other files named sqlite3-1.c, sqlite3-2.c, ..., sqlite3-7.c. In this way, all of the source code is contained within a single translation unit so that the compiler can do extra cross-procedure optimization, but no individual source file exceeds 32K lines in length.

How It All Fits Together

SQLite is modular in design. See the architectural description for details. Other documents that are useful in helping to understand how SQLite works include the file format description, the virtual machine that runs prepared statements, the description of how transactions work, and the overview of the query planner.

Decades of effort have gone into optimizing SQLite, both for small size and high performance. And optimizations tend to result in complex code. So there is a lot of complexity in the current SQLite implementation. It will not be the easiest library in the world to hack.

Key source code files

• sqlite.h.in - This file defines the public interface to the SQLite library. Readers will need to be familiar with this interface before trying to understand how the library works internally. This file is really a template that is transformed into the "sqlite3.h" deliverable using a script invoked by the makefile.

• sqliteInt.h - this header file defines many of the data objects used internally by SQLite. In addition to "sqliteInt.h", some subsystems inside of sQLite have their own header files. These internal interfaces are not for use by applications. They can and do change from one release of SQLite to the next.

• parse.y - This file describes the LALR(1) grammar that SQLite uses to parse SQL statements, and the actions that are taken at each step in the parsing process. The file is processed by the Lemon Parser Generator to produce the actual C code used for parsing.

• vdbe.c - This file implements the virtual machine that runs prepared statements. There are various helper files whose names begin with "vdbe". The VDBE has access to the vdbeInt.h header file which defines internal data objects. The rest of SQLite interacts with the VDBE through an interface defined by vdbe.h.

• where.c - This file (together with its helper files named by "where*.c") analyzes the WHERE clause and generates virtual machine code to run queries efficiently. This file is sometimes called the "query optimizer". It has its own private header file, whereInt.h, that defines data objects used internally.

• btree.c - This file contains the implementation of the B-Tree storage engine used by SQLite. The interface to the rest of the system is defined by "btree.h". The "btreeInt.h" header defines objects used internally by btree.c and not published to the rest of the system.

• pager.c - This file contains the "pager" implementation, the module that implements transactions. The "pager.h" header file defines the interface between pager.c and the rest of the system.

• os_unix.c and os_win.c - These two files implement the interface between SQLite and the underlying operating system using the run-time pluggable VFS interface.

• shell.c.in - This file is not part of the core SQLite library. This is the file that, when linked against sqlite3.a, generates the "sqlite3.exe" command-line shell. The "shell.c.in" file is transformed into "shell.c" as part of the build process.

• tclsqlite.c - This file implements the Tcl bindings for SQLite. It is not part of the core SQLite library. But as most of the tests in this repository are written in Tcl, the Tcl language bindings are important.

• test*.c - Files in the src/ folder that begin with "test" go into building the "testfixture.exe" program. The testfixture.exe program is an enhanced Tcl shell. The testfixture.exe program runs scripts in the test/ folder to validate the core SQLite code. The testfixture program (and some other test programs too) is built and run when you type "make test".

• VERSION, manifest, and manifest.uuid - These files define the current SQLite version number. The "VERSION" file is human generated, but the "manifest" and "manifest.uuid" files are automatically generated by the Fossil version control system.

There are many other source files. Each has a succinct header comment that describes its purpose and role within the larger system.

Verifying Code Authenticity

The manifest file at the root directory of the source tree contains either a SHA3-256 hash or a SHA1 hash for every source file in the repository. The name of the version of the entire source tree is just the SHA3-256 hash of the manifest file itself, possibly with the last line of that file omitted if the last line begins with "# Remove this line". The manifest.uuid file should contain the SHA3-256 hash of the manifest file. If all of the above hash comparisons are correct, then you can be confident that your source tree is authentic and unadulterated. Details on the format for the manifest files are available on the Fossil website.

The process of checking source code authenticity is automated by the makefile:

make verify-source

Or on windows:

nmake /f Makefile.msc verify-source

Using the makefile to verify source integrity is good for detecting accidental changes to the source tree, but malicious changes could be hidden by also modifying the makefiles.

Contacts

The main SQLite website is https://sqlite.org/ with geographically distributed backups at https://www2.sqlite.org/ and https://www3.sqlite.org/.

Contact the SQLite developers through the SQLite Forum. In an emergency, you can send private email to the lead developer at drh at sqlite dot org.